1. Field of the Invention
The present invention relates to an optical functional element of a structure, generally called a photonic crystal (hereinafter, referred to simply as xe2x80x9cphotonic crystalxe2x80x9d), in which plural media with different refractive indices are periodically arranged.
The present invention also relates to a method of producing the optical functional element (photonic crystal).
2. Related Background Art
Photonic crystals have artificial one- or multi-dimensional periodical structures (one-, two-, and three-dimensional) having similarities to solid crystals. More specifically, they have plural media with different refractive indices which are periodically arranged.
Conventional methods for fabricating photonic crystals of this type having plural media with different refractive indices which are periodically arranged include various methods, for example, dry etching, wet etching, fusion-lamination, sputtering, manipulation, self organization, application of lithography, etc.
However, the various conventional methods described above generally involve complicated processes and take a relatively long period of time. In addition, no simple method for fabricating two- or three-dimensional photonic crystals in particular has been known. The various methods described above are based on production technologies for semiconductors so that there is the problem in that it is difficult to use them to fabricate photonic crystals of a large area. Furthermore, another problem is that there are limitations on patterns that can be fabricated by such methods.
Basic properties and examples of operation of photonic crystals as well as conventional fabrication methods for photonic crystals are as described in JP 2001-272566 A entitled xe2x80x9cMethod for Manufacturing Photonic Crystalxe2x80x9d and detailed description will be omitted here.
The present invention has been made under the above-mentioned circumstances, and a first object of the present invention is to solve the problems with the conventional technologies and to provide an optical functional element which is a photonic crystal of a structure having plural media with different refractive indices periodically arranged therein.
A second object of the present invention is to provide a method of producing the optical functional element.
Other objects of the present invention will be apparent from the following description.
In order to attain the above-mentioned first object, a first aspect of the present invention provides an optical functional element comprising an aggregate of developed silver grains obtained by developing silver halide grains arranged so as to constitute a periodical structure. That is to say, the optical functional element of the present invention is a photonic crystal has such a feature that an aggregate of silver grains obtained by developing silver halide grains are arranged so as to constitute a periodical structure.
Here, the photonic crystal of the present invention has the following feature. That is, a photo-curing resin layer formed on a substrate in which silver halide grains are dispersed is first selectively exposed to radiation and then overall exposed to light to develop the silver halide grains dispersed in the photo-curing layer thereby forming an aggregate of developed silver arranged so as to construct the above-mentioned periodical structure.
In the photonic crystal of the present invention, the photo-curing resin layer in which silver halide grains are dispersed consists of a single layer or of plural layers. Where it consists of plural layers, it is preferred that an intermediate layer containing no silver halide grain be provided between any adjacent two of such layers.
Further, the photonic crystal of the present invention includes developing a material having a structure composed of a substrate, a binder layer on the substrate containing dispersed silver halide grains therein, and a photo-curing resin layer on at least one side of the binder layer by selectively exposing the photo-curing resin layer to radiation and then subjecting it to overall exposure to light to form an aggregate of developed silver which are arranged to construct the above-mentioned periodical structure.
The present invention can also provide an effective method for producing the above-mentioned photonic crystals. That is, the present invention can provide a method for producing a photonic crystal, comprising exposing and then selectively developing silver halide grains dispersed in a photo-curing resin layer formed on a substrate to form an aggregate of silver grains which are periodically arranged in the photo-curing resin layer.
Here, the above-mentioned photo-curing resin layer is preferably one to which infiltrating power (infiltrability) of a developer which develops the silver halide grains varies depending on the degree of photo-curing. Alternatively, the photo-curing resin layer is preferably one to which infiltrability of the developer varies by selective irradiation of the photo-curing resin layer with radiation.
Another effective method as a production method for photonic crystals is a method including developing a material having a structure composed of a substrate, a binder layer on the substrate containing dispersed silver halide grains therein, and a photo-curing resin layer on at least one side of the binder layer by selectively exposing the photo-curing resin layer to radiation and then subjecting it to overall exposure to light to form the aggregate of developed silver which are periodically arranged.
Still another effective method as a production method for photonic crystals is a method which comprises returning the photonic crystal formed as described above to the step of coating a photo-curing resin layer and again producing a single layer or plural layers of photonic crystal lattice on the previously fabricated single layer or plural layers of photonic crystal lattice on the photonic crystal. On this occasion, use of different lattice masks for the initial single layer or plural layers of photonic crystal lattice and for the single or plural layers of photonic crystal lattice formed so as to overlap the former enables fabrication of photonic crystals composed of multi-layer lattices with different angles.
In short, the method for producing a photonic crystal according to the present invention is just needed to form a periodical structure, by a difference in refractive index, between a region where developed silver exists and another region where no developed silver exists. No limitation is posed on its layer structure and lattice pattern, thus giving much freedom in choice.